JP-A-2012-142185 discusses improving the life performance of a lead-acid battery in an idling-stop mode at both normal and high temperatures. For this purpose, it proposes that: a Pb—Sn—Sb alloy layer is provided on the surface of a negative electrode grid; Li and Al are contained in electrolyte solution; and Na concentration of the electrolyte solution is set to be 0.04 mol/L or less.
In addition, for the electrode material of the negative electrode, 0.6 mass % of Ba sulfate is contained relative to 98.8 mass % of a lead powder. However, changing the Ba sulfate concentration from 0.6 mass % has not been considered.
In JP-A-2001-23682, the volume of an element of a sealed type lead-acid battery is defined by the height of electrode plates×the width of the electrode plates×the thickness of the element. It is disclosed that when the mass of a negative active material per unit volume of the element is 0.84 g/cm3 or more and 1.20 g/cm3 or less, the high-rate discharge performance improves. However, the influences of the Ba sulfate concentration and the Na concentration have not been examined.
JP-A-2003-178806 discusses the influences of the mass of the positive active material and the mass of the negative active material in a valve-regulated lead-acid battery, and shows an example in which the density of the positive active material is 4.20 g/cm3, and the mass ratio between the positive active material and the negative active material is 1.2.